Oricymba gongshanensis sp. nov. (Cymbellaceae; Bacillariophyceae), a new species from southwest China

Oricymba gongshanensis sp. nov. is identified as a new cymbelloid species, and described from a rock wall in Gongshan County, Yunnan Province, China. A detailed morphological description of the new species is presented, based on light and scanning electron microscopy. O. gongshanensis sp. nov. has the features that assign it to the genus Oricymba, including a thickened ridge positioned around the margin of the valve, presence of pore fields at the apices, a stigma with a single opening externally and two openings internally together with external distal raphe ends deflected dorsally. There are three features that easily distinguish the new species from all others in the genus. They include: 1) valves that are weakly asymmetrical about the apical axis, 2) presence of mostly biseriate striae and 3) areolae that are round to elliptical in shape. Among the currently described species of Oricymba, the new species is most similar to O. tianmuensis in valve shape, but is easily distinguished by the degree of asymmetry about the apical axis and presence of biseriate striae. These findings increase our understanding the morphology and distribution of the genus Oricymba in China.